Recently, use of equipment for a high-definition multimedia interface (HDMI) standard which is one of interface standards for transmitting uncompressed digital video and audio signals in an integrated manner has been widespread. The HDMI standard is the integration of a digital visual interface (DVI) which is a video interface standard for a personal computer (PC) and a display and a standard for an audio signal for audio/video (AV) home appliances. In the HDMI standard, a video signal and an audio signal are transmitted from a signal providing device to a device which outputs a video signal and an audio signal, e.g., a television (TV), without compressing them. Thus, a decoder chip or software is not needed. The HDMI standard may replace an existing analog terminal, and has been extensively applied to PCs, DVD players, HDTVs, etc.
A multimedia device may be connected to a multimedia device which provides a combined audio/video (A/V) signal via a cable and a connector supported by the HDMI standard so as to receive the combined A/V signal and output a video signal and an audio signal.
Conventionally, a conductor such as copper has been generally used as a cable according to the HDMI standard. However, when the cable is long, a signal loss rate is high and thus high video and sound quality of uncompressed digital video and audio signals is not secured.
Recently, this problem becomes more serious when the distance between a multimedia signal device providing a combined A/V signal and a multimedia output device (e.g., a projector, a large-sized screen, or a speaker) receiving the combined A/V signal from the multimedia signal device and outputting a video signal and an audio signal in a place such as a large-sized stadium, a lecture room, and a hall, as well as home, is several tens of meters or several hundreds of meters or more.
Thus, an optical and electrical composite multimedia cable has been recently introduced as a cable supported by the HDMI standard.
That is, the optical and electrical composite multimedia cable may include an optical unit having optical fibers and a conductor unit having a conductor. A video signal or an audio signal is transmitted via the optical fibers of the optical and electrical composite multimedia cable, and power or a control signal may be provided via the conductor.
Existing optical and electrical composite multimedia cables, a plastic optical fiber (POF) type cable and a glass optical fiber (GOF) type cable are classified according to the type of optical fibers have been introduced.
The size of a POF type cable is large due to the diameter of optical fibers thereof. In general, a GOF type cable may have a large diameter and have an asymmetric or flat cross section due to the diameter of a unit protecting GOF type optical fibers which are likely to be broken.
FIG. 5 is a cross-sectional view of a conventional POF type optical and electrical composite multimedia cable 10.
In the case of optical fibers of a POF type optical cable, a signal loss rate is high and thus a maximum signal loss measuring distance is limited to 250 m. Thus, each of the optical fibers should be produced in units of 500 meters or less for bi-directional measurement so that a failure in the optical fibers may be detected. Furthermore, when this cable is installed, the amount of the cable wasted is large and work continuity is low.
An optical unit 1 included in a flat hybrid optical and electrical cable and having POF type optical fibers is likely to deteriorate at high temperatures and freeze at low temperatures and thus characteristics thereof may be degraded after a long time. Thus, installation of the cable in an environment such as an outdoor place is restricted. Furthermore, each of POF type optical fibers has a large diameter, e.g., 300 μm or more, and thus minimizing the diameter of the cable 10 is limited.
The conventional optical and electrical composite multimedia cable 10 having a flat shape employs POFs and may be thus connected to a terminal in a simple manner, but directionality thereof is limited when it is bent and workability thereof may be low when pipe installation is conducted, due to the flat shape thereof.
A short width w of the optical and electrical composite multimedia cable 10 having the flat shape is small but a long width W thereof is large. Thus, it should be careful not to twist the cable 10 when the cable 10 is wound and a finished product has a large volume. When actually measured, the short width w of the cable 10 is 2.8 mm and the long width W thereof is 5.0 mm or more. Thus, the volume of a packed unit product for long-distance installation is significantly increased.
Due to the above reasons, for long-distance connection, it is preferable that an optical and electrical composite multimedia cable be manufactured to employ GOF type optical fibers to minimize the length of the cable wasted when installed, to sufficiently protect the optical fibers, to minimize the diameter of the cable, and not to be limited in terms of an installation direction when installed.
FIG. 6 illustrates a reference diagram of Japanese unexamined patent application publication No. 2013-218839.
As illustrated in FIG. 6, wires 15 are disposed around an optical fiber core 12 to decease the size of a cable. However, optical fiber cores 12a and 12b of a hybrid optical and electrical cable are in a coated state and are accommodated in a protective tube 13. Thus, an empty space inside the protective tube 13 is large, and the wires 15 disposed at an outer side of the protective tube 13 are spaced apart from each other. Therefore, an empty space between the wires 15 is significantly large and it is thus difficult to decrease the diameter of the cable 10.
FIG. 7 illustrates a reference diagram of Japanese unexamined patent application publication No. 2012-53121.
As illustrated in FIG. 7, a plurality of wires 15 are disposed around optical fiber cores 1, and covered with a skin 20.
However, when the wires 15 are disposed around the optical fiber cores 1 and covered with the skin 20 in a state in which the optical fiber cores 1 having a relatively small diameter are arranged at a center of a cable without being configured as separate units, it is difficult to sufficiently protect the optical fiber cores 1 and provide a flat mounting surface on the optical fiber cores 1 to dispose the wires 15 around the optical fiber cores 1. Accordingly, it is not easy to manufacture the cable to have a round cross section, and a process of manufacturing the cable may be complicated. Furthermore, an empty space between the optical fiber cores 1 may be large and thus the diameter of the cable is not easily decreased.